Orthopaedic knee prosthesis having controlled condylar curvature

ABSTRACT

An orthopaedic knee prosthesis includes a femoral component having a condyle surface. The condyle surface is defined by one or more radii of curvatures, which are controlled to reduce or delay the onset of anterior translation of the femoral component relative to a tibial bearing.

This application claims priority under 35 U.S.C. §120 to U.S. patentapplication Ser. No. 12/488,107 entitled “Orthopaedic Knee ProsthesisHaving Controlled Condylar Curvature,” by Joseph G. Wyss et al., whichwas filed on Jun. 19, 2009 and issued as U.S. Pat. No. 8,236,061 on Aug.7, 2012, and claimed priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Ser. No. 61/077,124 entitled “OrthopaedicKnee Prosthesis Having Controlled Condylar Curvature,” by Joseph G. Wysset al., which was filed on Jun. 30, 2008. The entirety of each of thoseapplications is hereby incorporated by reference.

CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION

Cross-reference is also made to U.S. Utility patent application Ser. No.12/165,579, entitled “Orthopaedic Femoral Component Having ControlledCondylar Curvature” by John L. Williams et al., which was filed on Jun.30, 2008; to U.S. Utility patent application Ser. No. 12/165,574, nowU.S. Pat. No. 8,192,498, entitled “Posterior Cruciate-RetainingOrthopaedic Knee Prosthesis Having Controlled Condylar Curvature” byChristel M. Wagner, which was filed on Jun. 30, 2008; to U.S. Utilitypatent application Ser. No. 12/165,575, now U.S. Pat. No. 8,187,335,entitled “Posterior Stabilized Orthopaedic Knee Prosthesis HavingControlled Condylar Curvature” by Joseph G. Wyss, which was filed onJun. 30, 2008; and to U.S. Utility patent application Ser. No.12/165,582, now U.S. Pat. No. 8,206,451, entitled “Posterior StabilizedOrthopaedic Prosthesis” by Joseph G. Wyss, which was filed on Jun. 30,2008; the entirety of each of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to orthopaedic prostheses, andparticularly to orthopaedic prostheses for use in knee replacementsurgery.

BACKGROUND

Joint arthroplasty is a well-known surgical procedure by which adiseased and/or damaged natural joint is replaced by a prosthetic joint.A typical knee prosthesis includes a tibial tray, a femoral component,and a polymer insert or bearing positioned between the tibial tray andthe femoral component. Depending on the severity of the damage to thepatient's joint, orthopaedic prostheses of varying mobility may be used.For example, the knee prosthesis may include a “fixed” tibial bearing incases wherein it is desirable to limit the movement of the kneeprosthesis, such as when significant soft tissue loss or damage ispresent. Alternatively, the knee prosthesis may include a “mobile”tibial bearing in cases wherein a greater degree of freedom of movementis desired. Additionally, the knee prosthesis may be a total kneeprosthesis designed to replace the femoral-tibial interface of bothcondyles of the patient's femur or a uni-compartmental (or uni-condylar)knee prosthesis designed to replace the femoral-tibial interface of asingle condyle of the patient's femur.

The type of orthopedic knee prosthesis used to replace a patient'snatural knee may also depend on whether the patient's posterior cruciateligament is retained or sacrificed (i.e., removed) during surgery. Forexample, if the patient's posterior cruciate ligament is damaged,diseased, and/or otherwise removed during surgery, a posteriorstabilized knee prosthesis may be used to provide additional supportand/or control at later degrees of flexion. Alternatively, if theposterior cruciate ligament is intact, a cruciate retaining kneeprosthesis may be used.

Typical orthopaedic knee prostheses are generally designed to duplicatethe natural movement of the patient's joint. As the knee is flexed andextended, the femoral and tibial components articulate and undergocombinations of relative anterior-posterior motion and relativeinternal-external rotation. However, the patient's surrounding softtissue also impacts the kinematics and stability of the orthopaedic kneeprosthesis throughout the joint's range of motion. That is, forcesexerted on the orthopaedic components by the patient's soft tissue maycause unwanted or undesirable motion of the orthopaedic knee prosthesis.For example, the orthopaedic knee prosthesis may exhibit an amount ofunnatural (paradoxical) anterior translation as the femoral component ismoved through the range of flexion.

In a typical orthopaedic knee prosthesis, paradoxical anteriortranslation may occur at nearly any degree of flexion, but particularlyat mid to late degrees of flexion. Paradoxical anterior translation canbe generally defined as an abnormal relative movement of a femoralcomponent on a tibial bearing wherein the contact “point” between thefemoral component and the tibial bearing “slides” anteriorly withrespect to the tibial bearing. This paradoxical anterior translation mayresult in loss of joint stability, accelerated wear, abnormal kneekinematics, and/or cause the patient to experience a sensation ofinstability during some activities.

SUMMARY

According to one aspect, an orthopaedic knee prosthesis may include afemoral component and a tibial bearing. The femoral component may have acondyle surface curved in the sagittal plane. The tibial bearing may bea bearing surface configured to articulate with the condyle surface ofthe femoral component. The condyle surface of the femoral component maybe configured to contact the bearing surface at a first contact point onthe condyle surface at a first degree of flexion less than about 30degrees. The condyle surface of the femoral component may be also beconfigured to contact the bearing surface at a second contact point onthe condyle surface at a second degree of flexion greater than about 45degrees. Additionally, the condyle surface of the femoral component maybe configured to contact the bearing surface at a third contact point onthe condyle surface at a third degree of flexion greater than the seconddegree of flexion. In some embodiments, the first degree of flexion maybe in the range of 0 degrees to 10 degrees, the second degree of flexionmay be in the range of 60 degrees to 70 degrees, and the third degree offlexion may be in the range of 80 degrees to 110 degrees. For example,in one particular embodiment, the first degree of flexion is about 5degrees, the second degree of flexion is about 65 degrees, and the thirddegree of flexion is about 90 degrees.

The condyle surface in the sagittal plane may have a first radius ofcurvature at the first contact point, a second radius curvature at thesecond contact point, and a third radius of curvature at the thirdcontact point. In some embodiments, the third radius of curvature may begreater than the second radius of curvature by at least 0.5 millimeters.Additionally, the condyle surface in the sagittal plane between thefirst contact point and the second contact point may include a pluralityof curved surface sections. Each curved surface section may have adifferent radius of curvature.

The plurality of curved surface sections may include an anterior-mostcurved surface section. In some embodiments, the radius of curvature ofthe anterior-most curved surface section may have a length greater thanthe radius of curvature of any other curved surface section of theplurality of curved surface sections. Additionally, in some embodiments,the length of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section may be less thanthe length of the radius of curvature of an anteriorly-adjacent curvedsurface section. For example, in some embodiments, the length of theradius of curvature of each curved surface section posterior to theanterior-most curved surface section is less than the length of theradius of curvature of an anteriorly-adjacent curved surface section bya distance in the range of 0.1 millimeters to 5 millimeters, in therange of 1 millimeters to 3 millimeters, and/or about 1 millimeter.

Each of the plurality of curved surface sections may subtend acorresponding angle. In some embodiments, each angle subtended by theplurality of curved surface sections being approximately equal. In otherembodiments, the angle subtended by each of the curved surface sectionsposterior to the anterior-most curved surface section may be less thanthe angle subtended by an anteriorly-adjacent curved surface section.For example, in some embodiments, the angle subtended by each of thecurved surface sections posterior to the anterior-most curved surfacesection may be less than the angle subtended by the anteriorly-adjacentcurved surface section by an amount in the range of 0.5 degrees to 5degrees. Additionally, in other embodiments, the angle subtended by eachof the curved surface sections posterior to the anterior-most curvedsurface section may be greater than the angle subtended by ananteriorly-adjacent curved surface section. For example, in someembodiments, the angle subtended by each of the curved surface sectionsposterior to the anterior-most curved surface section may be greaterthan the angle subtended by the anteriorly-adjacent curved surfacesection by an amount in the range of 0.5 degrees to 5 degrees.

According to another aspect, an orthopaedic knee prosthesis may includea femoral component and a tibial bearing. The femoral component may havea condyle surface curved in the sagittal plane. The tibial bearing maybe a bearing surface configured to articulate with the condyle surfaceof the femoral component. The condyle surface of the femoral componentmay be configured to contact the bearing surface at a first contactpoint on the condyle surface at a first degree of flexion in the rangeof 0 to about 30 degrees. The condyle surface of the femoral componentmay be also be configured to contact the bearing surface at a secondcontact point on the condyle surface at a second degree of flexion inthe range of 45 degrees to 90 degrees. The condyle surface in thesagittal plane between the first contact point and the second contactpoint may include at least five curved surface sections. Each curvedsurface section may have a radius of curvature having a length differentfrom any other curved surface section.

The plurality of curved surface sections may include an anterior-mostcurved surface section. The radius of curvature of the anterior-mostcurved surface section may have a length greater than the radius ofcurvature of any other curved surface section of the plurality of curvedsurface sections. Additionally, the length of the radius of curvature ofeach curved surface section posterior to the anterior-most curvedsurface section may be less than the length of the radius of curvatureof an anteriorly-adjacent curved surface section. For example, thelength of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section maybe less thanthe length of the radius of curvature of an anteriorly-adjacent curvedsurface section by a distance in the range of 1 millimeters to 3millimeters.

Each of the plurality of curved surface sections may subtend acorresponding angle. In some embodiments, the angle subtended by each ofthe curved surface sections posterior to the anterior-most curvedsurface section may be less than the angle subtended by ananteriorly-adjacent curved surface section. In other embodiments, theangle subtended by each of the curved surface sections posterior to theanterior-most curved surface section may be greater than the anglesubtended by an anteriorly-adjacent curved surface section.

According to another aspect, an orthopaedic knee prosthesis may includea femoral component and a tibial bearing. The femoral component may havea condyle surface curved in the sagittal plane. The tibial bearing maybe a bearing surface configured to articulate with the condyle surfaceof the femoral component. The condyle surface of the femoral componentmay be configured to contact the bearing surface at a first contactpoint on the condyle surface at a first degree of flexion in the rangeof 0 to about 30 degrees. The condyle surface of the femoral componentmay be also be configured to contact the bearing surface at a secondcontact point on the condyle surface at a second degree of flexion inthe range of 45 degrees to 90 degrees. The condyle surface in thesagittal plane between the first contact point and the second contactpoint may include at least five curved surface sections. Each curvedsurface section may subtend a corresponding, substantially equal angleand may have a radius of curvature different from any other curvedsurface section.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is an exploded perspective view of one embodiment of anorthopaedic knee prosthesis;

FIG. 2 is an exploded perspective view of another embodiment of anorthopaedic knee prosthesis;

FIG. 3 is a cross-sectional view of one embodiment of a femoralcomponent and tibial bearing of FIG. 1 taken generally along sectionlines 2-2 and having the femoral component articulated to a first degreeof flexion;

FIG. 4 is a cross-sectional view of a femoral component and tibialbearing of FIG. 3 having the femoral component articulated to a seconddegree of flexion;

FIG. 5 is a cross-sectional view of a femoral component and tibialbearing of FIG. 3 having the femoral component articulated to a thirddegree of flexion;

FIG. 6 is a cross-sectional view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 7 is a cross-sectional view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 8 is a graph of the anterior-posterior translation of a simulatedfemoral component having an increased radius of curvature located atvarious degrees of flexion;

FIG. 9 is a graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion;

FIG. 10 is a graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion; and

FIG. 11 is a graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthis disclosure in reference to both the orthopaedic implants describedherein and a patient's natural anatomy. Such terms have well-understoodmeanings in both the study of anatomy and the field of orthopaedics. Useof such anatomical reference terms in the specification and claims isintended to be consistent with their well-understood meanings unlessnoted otherwise.

Referring now to FIG. 1, in one embodiment, an orthopaedic kneeprosthesis 10 includes a femoral component 12, a tibial bearing 14, anda tibial tray 16. The femoral component 12 and the tibial tray 16 areillustratively formed from a metallic material such as cobalt-chromiumor titanium, but may be formed from other materials, such as a ceramicmaterial, a polymer material, a bio-engineered material, or the like, inother embodiments. The tibial bearing 14 is illustratively formed from apolymer material such as a ultra-high molecular weight polyethylene(UHMWPE), but may be formed from other materials, such as a ceramicmaterial, a metallic material, a bio-engineered material, or the like,in other embodiments.

As discussed in more detail below, the femoral component 12 isconfigured to articulate with the tibial bearing 14, which is configuredto be coupled with the tibial tray 16. In the illustrative embodiment ofFIG. 1, the tibial bearing 14 is embodied as a rotating or mobile tibialbearing and is configured to rotate relative to the tibial tray 16during use. However, in other embodiments, the tibial bearing 14 may beembodied as a fixed tibial bearing, which may be limited or restrictedfrom rotating relative the tibial tray 16.

The tibial tray 16 is configured to be secured to a surgically-preparedproximal end of a patient's tibia (not shown). The tibial tray 16 may besecured to the patient's tibia via use of bone adhesive or otherattachment means. The tibial tray 16 includes a platform 18 having a topsurface 20 and a bottom surface 22. Illustratively, the top surface 20is generally planar and, in some embodiments, may be highly polished.The tibial tray 16 also includes a stem 24 extending downwardly from thebottom surface 22 of the platform 18. A cavity or bore 26 is defined inthe top surface 20 of the platform 18 and extends downwardly into thestem 24. The bore 26 is formed to receive a complimentary stem of thetibial insert 14 as discussed in more detail below.

As discussed above, the tibial bearing 14 is configured to be coupledwith the tibial tray 16. The tibial bearing 14 includes a platform 30having an upper bearing surface 32 and a bottom surface 34. In theillustrative embodiment wherein the tibial bearing 14 is embodied as arotating or mobile tibial bearing, the bearing 14 includes a stem 36extending downwardly from the bottom surface 32 of the platform 30. Whenthe tibial bearing 14 is coupled to the tibial tray 16, the stem 36 isreceived in the bore 26 of the tibial tray 16. In use, the tibialbearing 14 is configured to rotate about an axis defined by the stem 36relative to the tibial tray 16. In embodiments wherein the tibialbearing 14 is embodied as a fixed tibial bearing, the bearing 14 may ormay not include the stem 22 and/or may include other devices or featuresto secure the tibial bearing 14 to the tibial tray 16 in a non-rotatingconfiguration.

The upper bearing surface 32 of the tibial bearing 14 includes a medialbearing surface 42 and a lateral bearing surface 44. The medial andlateral bearing surfaces 42, 44 are configured to receive or otherwisecontact corresponding medial and lateral condyles of the femoralcomponent 12 as discussed in more detail below. As such, each of thebearing surface 42, 44 has a concave contour.

The femoral component 12 is configured to be coupled to asurgically-prepared surface of the distal end of a patient's femur (notshown). The femoral component 12 may be secured to the patient's femurvia use of bone adhesive or other attachment means. The femoralcomponent 12 includes an outer, articulating surface 50 having a pair ofmedial and lateral condyles 52, 54. The condyles 52, 54 are spaced apartto define an intracondyle opening 56 therebetween. In use, the condyles52, 54 replace the natural condyles of the patient's femur and areconfigured to articulate on the corresponding bearing surfaces 42, 44 ofthe platform 30 of the tibial bearing 14.

The illustrative orthopaedic knee prosthesis 10 of FIG. 1 is embodied asa posterior cruciate-retaining knee prosthesis. That is, the femoralcomponent 12 is embodied as a posterior cruciate-retaining kneeprosthesis and the tibial bearing 14 is embodied as a posteriorcruciate-retaining tibial bearing 14. However, in other embodiments, theorthopaedic knee prosthesis 10 may be embodied as a posteriorcruciate-sacrificing knee prosthesis as illustrated in FIG. 2.

In such embodiments, the tibial bearing 14 is embodied as a posteriorstabilizing tibial bearing and includes a spine 60 extending upwardlyfrom the platform 30. The spine 60 is positioned between the bearingsurfaces 42, 44 and includes an anterior side 62 and a posterior side 64having a cam surface 66. In the illustrative embodiment, the cam surface66 has a substantially concave curvature. However, spines 60 includingcam surfaces 66 having other geometries may be used in otherembodiments. For example, a tibial bearing including a spine having asubstantially “S”-shaped cross-sectional profile, such as the tibialbearing described in U.S. patent application Ser. No. 12/165,582,entitled “Posterior Stabilized Orthopaedic Prosthesis” by Joseph G.Wyss, et al., which is hereby incorporated by reference, may be used inother embodiments.

Additionally, in such embodiments, the femoral component 12 is embodiedas a posterior stabilized femoral component and includes an intracondylenotch or recess 57 (rather than an opening 56). A posterior cam 80(shown in phantom) and an anterior cam 82 are positioned in theintracondyle notch 57. The posterior cam 80 is located toward theposterior side of the femoral component 12 and includes a cam surface 86configured to engage or otherwise contact the cam surface 66 of thespine 60 of the tibial bearing 14 during flexion.

It should be appreciated that although the orthopaedic knee prosthesis10 may be embodied as either a posterior cruciate-retaining or acruciate-sacrificing knee prosthesis, the femoral component 12 and thetibial bearing 14 of the knee prosthesis 10 are discussed below, andillustrated in the remaining figures, in regard to a posteriorcruciate-retaining knee prosthesis with the understanding that suchdescription is equally applicable to those embodiments wherein theorthopaedic knee prosthesis 10 is embodied as a posteriorcruciate-sacrificing (posterior stabilized) orthopaedic knee prosthesis.

It should be appreciated that the illustrative orthopaedic kneeprosthesis 10 is configured to replace a patient's right knee and, assuch, the bearing surface 42 and the condyle 52 are referred to as beingmedially located; and the bearing surface 44 and the condyle 54 arereferred to as being laterally located. However, in other embodiments,the orthopaedic knee prosthesis 10 may be configured to replace apatient's left knee. In such embodiments, it should be appreciated thatthe bearing surface 42 and the condyle 52 may be laterally located andthe bearing surface 44 and the condyle 54 may be medially located.Regardless, the features and concepts described herein may beincorporated in an orthopaedic knee prosthesis configured to replaceeither knee joint of a patient.

Referring now to FIGS. 3-5, the femoral component 12 is configured toarticulate on the tibial bearing 14 during use. Each condyle 52, 54 ofthe femoral component 12 includes a condyle surface 100, which isconvexly curved in the sagittal plane and configured to contact therespective bearing surface 42, 44. For example, in one embodiment asshown in FIG. 3, when the orthopaedic knee prosthesis 10 is in extensionor is otherwise not in flexion (e.g., a flexion of about 0 degrees), thecondyle surface 100 of the condyle 52 contacts the bearing surface 42(or bearing surface 44 in regard to condyle 54) at one or more contactpoints 102 on the condyle surface 100.

Additionally, as the orthopaedic knee prosthesis 10 is articulatedthrough the middle degrees of flexion, the femoral component 12 contactsthe tibial bearing 14 at one or more contact points on the condylesurface 100. For example, in one embodiment as illustrated in FIG. 4,when the orthopaedic knee prosthesis 10 is articulated to a middledegree of flexion (e.g., at about 45 degrees), the condyle surface 100contacts the bearing surface 42 at one or more contact points 104 on thecondyle surface 100. Similarly, as the orthopaedic knee prosthesis 10 isarticulated to a late degree of flexion (e.g., at about 70 degrees offlexion), the condyle surface 100 contacts the bearing surface 42 at oneor more contact points 106 on the condyle surface 100 as illustrated inFIG. 5. It should be appreciated, of course, that the femoral component12 may contact the tibial bearing 14 at a plurality of contact points onthe condyle surface 100 at any one particular degree of flexion.However, for clarity of description, only the contact points 102, 104,106 have been illustrated in FIGS. 3-5, respectively.

The orthopaedic knee prosthesis 10 is configured such that the amount ofparadoxical anterior translation of the femoral component 12 relative tothe tibial bearing 14 may be reduced or otherwise delayed to a later(i.e., larger) degree of flexion. In particular, as discussed in moredetail below, the condyle surface 100 of one or both of the condyles 52,54 has particular geometry or curvature configured to reduce and/ordelay anterior translations and, in some embodiments, promote“roll-back” or posterior translation, of the femoral component 12. Itshould be appreciated that by delaying the onset of paradoxical anteriortranslation of the femoral component 12 to a larger degree of flexion,the overall occurrence of paradoxical anterior translation may bereduced during those activities of a patient in which deep flexion isnot typically obtained.

In a typical orthopaedic knee prosthesis, paradoxical anteriortranslation may occur whenever the knee prosthesis is positioned at adegree of flexion greater than zero degrees. The likelihood of anteriortranslation generally increases as the orthopaedic knee prosthesis isarticulated to larger degrees of flexion, particularly in themid-flexion range. In such orientations, paradoxical anteriortranslation of the femoral component on the tibial bearing can occurwhenever the tangential (traction) force between the femoral componentand the tibial bearing fails to satisfy the following equation:T<μN  (1)

wherein “T” is the tangential (traction) force, “μ” is the coefficientof friction of the femoral component and the tibial bearing, and “N” isthe normal force between the femoral component and the tibial bearing.As a generalization, the tangential (traction) force between the femoralcomponent and the tibial bearing can be defined asT=M/R  (2)

wherein “T” is the tangential (traction) force between the femoralcomponent and the tibial bearing, “M” is the knee moment, and “R” is theradius of curvature in the sagittal plane of the condyle surface incontact with the tibial bearing at the particular degree of flexion. Itshould be appreciated that equation (2) is a simplification of thegoverning real-world equations, which does not consider such otherfactors as inertia and acceleration. Regardless, the equation (2)provides insight that paradoxical anterior translation of an orthopaedicknee prosthesis may be reduced or delayed by controlling the radius ofcurvature of the condyle surface of the femoral component. That is, bycontrolling the radius of curvature of the condyle surface (e.g.,increasing or maintaining the radius of curvature), the right-hand sideof equation (2) may be reduced, thereby decreasing the value of thetangential (traction) force and satisfying the equation (1). Asdiscussed above, by ensuring that the tangential (traction) forcesatisfies equation (1), paradoxical anterior translation of the femoralcomponent on the tibial bearing may be reduced or otherwise delayed to agreater degree of flexion.

Based on the above analysis, to reduce or delay the onset of paradoxicalanterior translation, the geometry of the condyle surface 100 of one orboth of the condyles 52, 54 of the femoral component 12 is controlled.For example, in some embodiments, the radius of curvature of the condylesurface 100 is controlled such that the radius of curvature is heldconstant over a range of degrees of flexion and/or is increased in theearly to mid flexion ranges. Comparatively, typical femoral componentshave decreasing radii of curvatures beginning at the distal radius ofcurvature (i.e., at about 0 degrees of flexion). However, it has beendetermined that by maintaining a relatively constant radius of curvature(i.e., not decreasing the radius of curvature) over a predeterminedrange of degrees of early to mid-flexion and/or increasing the radius ofcurvature over the predetermined range of degrees of flexion may reduceor delay paradoxical anterior translation of the femoral component 12.

Additionally, in some embodiments, the condyle surface 100 is configuredor designed such that the transition between discrete radii of curvatureof the condyle surface 100 is gradual. That is, by graduallytransitioning between the discrete radii of curvature, rather thanabrupt transitions, paradoxical anterior translation of the femoralcomponent 12 may be reduced or delayed. Further, in some embodiments,the rate of change in the radius of curvature of the condyle surface inthe early to mid flexion ranges (e.g., from about 0 degrees to about 90degrees) is controlled such that the rate of change is less than apredetermined threshold. That is, it has been determined that if therate of change of the radius of curvature of the condyle surface 100 isgreater than the predetermined threshold, paradoxical anteriortranslation may occur.

Accordingly, in some embodiments as illustrated in FIGS. 6-12, thecondyle surface 100 of the femoral component 12 has an increased radiusof curvature in early to middle degrees of flexion. By increasing theradius of curvature, paradoxical anterior translation may be reduced ordelayed to a later degree of flexion. The amount of increase between theradius of curvature R2 and the radius of curvature R3 (see FIGS. 6 and7), as well as, the degree of flexion on the condyle surface 100 atwhich such increase occurs has been determined to affect the occurrenceof paradoxical anterior translation. As discussed in more detail in theU.S. patent application Ser. No. 12/165,579, entitled “OrthopaedicFemoral Prosthesis Having Controlled Condylar Curvature”, which wasfiled concurrently herewith and is hereby incorporated by reference,multiple simulations of various femoral component designs were performedusing the LifeMOD/Knee Sim, version 1007.1.0 Beta 16 software program,which is commercially available from LifeModeler, Inc. of San Clemente,Calif., to analyze the effect of increasing the radius of curvature ofthe condyle surface of the femoral components in early and mid flexion.Based on such analysis, it has been determined that paradoxical anteriortranslation of the femoral component relative to the tibial bearing maybe reduced or otherwise delayed by increasing the radius of curvature ofthe condyle surface by an amount in the range of about 0.5 millimetersto about 5 millimeters or more at a degree of flexion in the range ofabout 30 degrees of flexion to about 90 degrees of flexion.

For example, the graph 200 illustrated in FIG. 8 presents the results ofa deep bending knee simulation using a femoral component wherein theradius of curvature of the condyle surface is increased by 0.5millimeters (i.e., from 25.0 millimeters to 25.5 millimeters) at 30degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion,and at 90 degrees of flexion. Similarly, the graph 300 illustrated inFIG. 9 presents the results of a deep bending knee simulation using afemoral component wherein the radius of curvature of the condyle surfaceis increased by 1.0 millimeters (i.e., from 25.0 millimeters to 26.0millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70degrees of flexion, and at 90 degrees of flexion. The graph 400illustrated in FIG. 10 presents the results of a deep bending kneesimulation using a femoral component wherein the radius of curvature ofthe condyle surface is increased by 2.0 millimeters (i.e., from 25.0millimeters to 27.0 millimeters) at 30 degrees of flexion, at 50 degreesof flexion, at 70 degrees of flexion, and at 90 degrees of flexion.Additionally, the graph 500 illustrated in FIG. 11 presents the resultsof a deep bending knee simulation using a femoral component wherein theradius of curvature of the condyle surface is increased by 5.0millimeters (i.e., from 25.0 millimeters to 26.0 millimeters) at 30degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion,and at 90 degrees of flexion.

In the graphs 200, 300, 400, 500, the condylar lowest or most distalpoints (CLP) of the medial condyle (“med”) and the lateral condyle(“lat”) of the femoral component are graphed as a representation of therelative positioning of the femoral component to the tibial bearing. Assuch, a downwardly sloped line represents roll-back of the femoralcomponent on the tibial bearing and an upwardly sloped line representsanterior translation of the femoral component on the tibial bearing.

As illustrated in the graphs 200, 300, 400, 500, anterior sliding of thefemoral component was delayed until after about 100 degrees of flexionin each of the embodiments; and the amount of anterior translation waslimited to less than about 1 millimeter. In particular, “roll-back” ofthe femoral component on the tibial bearing was promoted by largerincreases in the radius of curvature of the condyle surface at earlierdegrees of flexion. Of course, amount of increase in the radius ofcurvature and the degree of flexion at which such increase is introducedis limited by other factors such as the anatomical joint space of thepatient's knee, the size of the tibial bearing, and the like.Regardless, based on the simulations reported in the graphs 200, 300,400, 500, paradoxical anterior translation of the femoral component onthe tibial bearing can be reduced or otherwise delayed by increasing theradius of curvature of the condyle surface of the femoral componentduring early to mid flexion.

Accordingly, referring back to FIGS. 6 and 7, the condyle surface 100 inthe sagittal plane is formed in part from a number of curved surfacesections 102, 104, 106, 108, the sagittal ends of each of which aretangent to the sagittal ends of any adjacent curved surface section ofthe condyles surface 100. Each curved surface section 102, 106, 108 isdefined by a radius of curvature. In particular, the curved surfacesection 102 is defined by a radius of curvature R1, the curved surfacesection 106 is defined by a radius of curvature R3, and the curvedsurface section 108 is defined by a radius of curvature R4. In addition,as discussed in more detail below, the curved surface section 104 isdesigned to provide a gradual transition from the first radius ofcurvature R1 to a second radius of curvature R2. To do so, the curvedsurface section 104 is defined by a plurality of curved surface sections110, 120, each of which is defined by a separate radius of curvature R5.

As discussed above, the condyle surface 100 of the femoral component 12is configured such that the radius of curvature R3 of the curved surfacesection 106 is greater than the radius of curvature R2 of the curvedsurface section 104. In one embodiment, the radius of curvature R3 isgreater than the radius of curvature R2 by 0.5 millimeters or more. Inanother embodiment, the radius of curvature R3 is greater than theradius of curvature R2 by 2 millimeters or more. In another embodiment,the radius of curvature R3 is greater than the radius of curvature R2 by2 millimeters or more. In a particular embodiment, the radius ofcurvature R3 is greater than the radius of curvature R2 by at least 5millimeters or more. It should be appreciated, however, that theparticular increase of radius of curvature between R2 and R3 may bebased on or scaled to the particular size of the femoral component 12 insome embodiments.

Each of the curved surface sections 102, 104, 106, 108 contacts thebearing surface 42 (or 44) of the tibial bearing 14 through differentranges of degrees of flexion. For example, the curved surface section102 extends from an earlier degree of flexion θ1 to a later degree offlexion θ2. The curved surface section 104 extends from the degree offlexion θ2 to a later degree of flexion θ3. The curved surface section106 extends from the degree of flexion θ3 to a later degree of flexionθ4.

For example, in one embodiment, the curved surface section 102 mayextend from a degree of flexion θ1 of about −10 degrees (i.e., 10degrees of hyperextension) to a degree of flexion θ2 of about 5 degreesof flexion. The curved surface section 104 extends from the degree offlexion θ2 of about 5 degrees of flexion to a degree of flexion θ3 ofabout 65 degrees of flexion. The curved surface section 106 extends fromthe degree of flexion θ3 of about 65 degrees of flexion to a degree offlexion θ4 of about 90 degrees of flexion and the curved surface section108 extends from the degree of flexion θ4 of about 90 degrees of flexionto a degree of flexion θ5 of about 104 degrees of flexion.

It should be appreciated, however, that each of the curved surfacesections 102, 104, 106, 108 may extend from degrees of flexion differentfrom those discussed above. For example, the particular degrees offlexion through which the curved surface sections 102, 104, 106, 108extend may be based or otherwise determined based on the type of femoralcomponent 12 (e.g., cruciate-retaining or posterior stabilized), thesize of the femoral component 12, and/or the like.

As discussed above, the curved surface section 104 is designed togradually transition from the radius of curvature R1 to the radius ofcurvature R2. To do so, in one embodiment as illustrated in FIG. 5, thecurved surface section 104 is defined by a plurality of curved surfacesections 110. In the illustrative embodiment of FIG. 5, the curvedsurface section 104 is defined by six curved surface sections 110A,110B, 110C, 110D, 110E, 110F, but may be defined by or otherwise includemore or less curved surface sections 110 in other embodiments. Theparticular number of curved surface sections 110 used may be based on,for example, the size of the angle subtended by the curved surfacesection 104.

Each of the curved surface sections 110 of the condyle surface 100contacts the bearing surface 42 (or 44) of the tibial bearing 14 throughdifferent ranges of degrees of flexion. For example, the curved surfacesection 110A extends from the degree of flexion θ2 to a later degree offlexion θC1, the curved surface section 110B extends from the degree offlexion θC1 to a later degree of flexion θC2, the curved surface section110C extends from the degree of flexion θC2 to a later degree of flexionθC3, the curved surface section 110D extends from the degree of flexionθC3 to a later degree of flexion θC4, the curved surface section 110Eextends from the degree of flexion θC4 to a later degree of flexion θC5,and the curved surface section 110F extends from the degree of flexionθC5 to the later degree of flexion θ3.

In the illustrative embodiment of FIG. 6, each of the curved surfacesections 110 extend substantially equal degrees of flexion. That is, thedegrees of flexion between θ2 and θC1, θC1 and θC2, between θC2 and θC3,between θC3 and θC4, between θC4 and θC5, and between θC5 and θ3 aresubstantially equal. In one particular embodiment, each curved surfacesection 110 extends for about 10 degrees. However, in other embodiments,each curved surface section 110 may extend a greater or lesser amount.In particular, in one embodiment, each curved surface section extend(i.e., subtend an angle) from about 1 degree to about 15 degrees.

Each of the curved surface sections 110 is defined by a radius ofcurvature R5. That is, the curved surface section 110A is defined by aradius of curvature R5A, the curved surface section 110B is defined by aradius of curvature R5B, the curved surface section 110C is defined by aradius of curvature R5C, the curved surface section 110D is defined by aradius of curvature R5D, the curved surface section 110E is defined by aradius of curvature R5E, and the curved surface section 110F is definedby a radius of curvature R5F. Each radius of curvature R5 is smaller(i.e., has a shorter length) than the anteriorly-adjacent radius ofcurvature R5. That is, R5F is smaller than R5E, R5E is smaller than R5D,R5D is smaller than R5C, R5C is smaller than R5B, and R5B is smallerthan R5A. For example, in one embodiment, each radius of curvature R5may have a length shorter than the anteriorly-adjacent radius ofcurvature R5 by an amount in the range of about 0.1 millimeters to about5 millimeters. However, in other embodiments, each radius of curvatureR5 may have a length shorter than the anteriorly-adjacent radius ofcurvature R5 by an amount greater or less than such values. Theparticular length of each radius of curvature R5 may be determined basedon the particular application, the length of the curved surface section104, an defined equation, and/or the like.

Referring now to FIG. 7, in another embodiment, the curved surfacesection 104 may be formed by a plurality of curved surface sections 120,each of which may extend a different amount of degrees (i.e., subtendangles of different sizes). For example, in the illustrative embodimentof FIG. 7, the curved surface section 104 is defined by ten curvedsurface sections 120A, 120B, 120C, 120D, 120E, 120F, 120G, 120H, 1201,120J. The curved surface section 120A extends from the degree of flexionθ1 to a later degree of flexion θC1, the curved surface section 120Bextends from the degree of flexion θC1 to a later degree of flexion θC2,the curved surface section 120C extends from the degree of flexion θC2to a later degree of flexion θC3, the curved surface section 120Dextends from the degree of flexion θC3 to a later degree of flexion θC4,the curved surface section 120E extends from the degree of flexion θC4to a later degree of flexion θC5, the curved surface section 120Fextends from the degree of flexion θC5 to a later degree of flexion θC6,the curved surface section 120G extends from the degree of flexion θC6to a later degree of flexion θC7, the curved surface section 120Hextends from the degree of flexion θC7 to a later degree of flexion θC8,the curved surface section 120I extends from the degree of flexion θC8to a later degree of flexion θC9, and the curved surface section 120Jextends from the degree of flexion θC9 to the later degree of flexionθ3.

As discussed above, each of the curved surface sections 120 extenddifferent degrees of flexion. That is, the degrees of flexion between θ2and θC1, θC1 and θC2, between θC2 and θC3, between θC3 and θC4, betweenθC4 and θC5, between θC5 and θC6, between θC6 and θC7, between θC7 andθC8, between θC8 and θC9, and between θC9 and θ3 are different from eachother. In some embodiments, each curved surface section 120 subtends anangle that is less than the angle subtended by the anteriorly-adjacentsection 120. For example, in the illustrative embodiment of FIG. 7, thecurved surface section 120A extends for about 10 degrees, the curvedsurface section 120B extends for about 9 degrees, the curved surfacesection 120C extends for about 8 degrees, the curved surface section120D extends for about 7 degrees, the curved surface section 120Eextends for about 6 degrees, the curved surface section 120F extends forabout 5 degrees, the curved surface section 120G extends for about 4degrees, the curved surface section 120H extends for about 3 degrees,the curved surface section 120I extends for about 2 degrees, and thecurved surface section 120J extends for about 1 degree.

Although each curved surface section 120 subtends an angle 1 degree lessthan the anteriorly-adjacent section 120 in the illustrative embodimentof FIG. 7, the curved surface sections 120 may subtend angles that areless than the anteriorly adjacent section 120 by an amount greater than1 degree in other embodiments. Additionally, in other embodiments, eachcurved surface section 120 may subtend an angle that is greater than theangle subtended by the anteriorly-adjacent section 120. For example,each curved surface section 120 may subtend an angle that is greaterthan the angle subtended by the anteriorly-adjacent section 120 by about0.5, 1, or more degrees in some embodiments. Further, in someembodiments, each of the curved surface sections 120 may subtend anglesof various sizes. That, each curved surface section 120 may be greaterthan or less than the anteriorly-adjacent curved surface 120 in someembodiments.

The overall shape and design of the condyle surface 100 of the femoralcomponent 12 has been described above in regard to a single condyle 52,54 of the femoral component 12. It should be appreciated that in someembodiments both condyles 52, 54 of the femoral component 12 may besymmetrical and have similar condyle surfaces 100. However, in otherembodiments, the condyles 52, 54 of the femoral component 12 may beasymmetrical. That is, each condyle 52, 54 may have a condyle surface100 having the features described herein but being asymmetrical to theother condyle 52, 54.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the devices and assemblies describedherein. It will be noted that alternative embodiments of the devices andassemblies of the present disclosure may not include all of the featuresdescribed yet still benefit from at least some of the advantages of suchfeatures. Those of ordinary skill in the art may readily devise theirown implementations of the devices and assemblies that incorporate oneor more of the features of the present invention and fall within thespirit and scope of the present disclosure as defined by the appendedclaims.

The invention claimed is:
 1. An orthopaedic knee prosthesis comprising:a femoral component having a condyle surface that is curved in thesagittal plane, the condyle surface including: an inferior-most point, adistal surface extending posteriorly from the inferior-most point to asuperior-most point, the distal surface defining an arc having amagnitude of about 30 degrees between the inferior-most point of thecondyle surface and the superior-most point of the distal surface, afirst posterior surface connected to the superior-most point of thedistal surface, the first posterior surface extending superiorly andposteriorly away from the distal surface to define an arc having amagnitude of about 15 degrees, and a second posterior surface having aninferior point connected to a superior-most point of the first posteriorsurface, the second posterior surface extending superiorly from theinferior point to a superior-most point, wherein (i) the condyle surfacein the sagittal plane has a first radius of curvature at a first pointon the distal surface, (ii) the condyle surface in the sagittal planehas a second radius of curvature at a second point on the secondposterior surface, and (iii) the condyle surface in the sagittal planehas a third radius of curvature at a third point on the second posteriorsurface positioned between the second point and the superior-most pointof the second posterior surface, the third radius of curvature beinggreater than the second radius of curvature by at least 0.5 millimeters,wherein the condyle surface in the sagittal plane between the firstpoint and the second point includes a plurality of curved surfacesections, each curved surface section having a different radius ofcurvature.
 2. The orthopaedic knee prosthesis of claim 1, wherein theplurality of curved surface sections include an anterior-most curvedsurface section, the radius of curvature of the anterior-most curvedsurface section having a length greater than the radius of curvature ofany other curved surface section of the plurality of curved surfacesections.
 3. The orthopaedic knee prosthesis of claim 2, wherein thelength of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section is less than thelength of the radius of curvature of an anteriorly-adjacent curvedsurface section.
 4. The orthopaedic knee prosthesis of claim 3, whereinthe length of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section is less than thelength of the radius of curvature of an anteriorly-adjacent curvedsurface section by a distance in the range of 0.1 millimeters to 5millimeters.
 5. The orthopaedic knee prosthesis of claim 4, wherein thelength of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section is less than thelength of the radius of curvature of an anteriorly-adjacent curvedsurface section by a distance in the range of 1 millimeters to 3millimeters.
 6. The orthopaedic knee prosthesis of claim 5, wherein thelength of the radius of curvature of each curved surface sectionposterior to the anterior-most curved surface section is less than thelength of the radius of curvature of an anteriorly-adjacent curvedsurface section by about 1 millimeter.
 7. The orthopaedic kneeprosthesis of claim 1, wherein each of the plurality of curved surfacesections subtends a corresponding angle, each angle subtended by theplurality of curved surface sections being approximately equal.
 8. Theorthopaedic knee prosthesis of claim 1, wherein (i) the plurality ofcurved surface sections include an anterior-most curved surface sectionand (ii) each of the plurality of curved surface sections subtends acorresponding angle, the angle subtended by each of the curved surfacesections posterior to the anterior-most curved surface section beingless than the angle subtended by an anteriorly-adjacent curved surfacesection.
 9. The orthopaedic knee prosthesis of claim 8, wherein theangle subtended by each of the curved surface sections posterior to theanterior-most curved surface section is less than the angle subtended bythe anteriorly-adjacent curved surface section by an amount in the rangeof 0.5 degrees to 5 degrees.
 10. The orthopaedic knee prosthesis ofclaim 1, wherein (i) the plurality of curved surface sections include ananterior-most curved surface section and (ii) each of the plurality ofcurved surface sections subtends a corresponding angle, the anglesubtended by each of the curved surface sections posterior to theanterior-most curved surface section being greater than the anglesubtended by an anteriorly-adjacent curved surface section.
 11. Theorthopaedic knee prosthesis of claim 10, wherein the angle subtended byeach of the curved surface sections posterior to the anterior-mostcurved surface section is greater than the angle subtended by theanteriorly-adjacent curved surface section by an amount in the range of0.5 degrees to 5 degrees.
 12. The orthopaedic knee prosthesis of claim11, further comprising: a tibial bearing having a bearing surfaceconfigured to articulate with the condyle surface of the femoralcomponent, wherein the condyle surface of the femoral component (i)contacts the bearing surface at the first point on the distal surface ata first degree of flexion that is in the range of 0 degrees to 10degrees, (ii) contacts the bearing surface at the second point on thesecond posterior surface at a second degree of flexion that is in therange of 60 degrees to 70 degrees, and (iii) contacts the bearingsurface at the third point on the second posterior surface at a thirddegree of flexion that is in the range of 80 degrees to 110 degrees. 13.The orthopaedic knee prosthesis of claim 12, wherein the first degree offlexion is about 5 degrees, the second degree of flexion is about 65degrees, and the third degree of flexion is about 90 degrees.
 14. Anorthopaedic knee prosthesis comprising: a femoral component having acondyle surface that is curved in the sagittal plane, the condylesurface including: an inferior-most point, a distal surface extendingposteriorly from the inferior-most point to a superior-most point, thedistal surface defining an arc having a magnitude of about 30 degreesbetween the inferior-most point of the condyle surface and thesuperior-most point of the distal surface, a first posterior surfaceconnected to the superior-most point of the distal surface, the firstposterior surface extending superiorly and posteriorly away from thedistal surface to define an arc having a magnitude of about 15 degrees,and a second posterior surface having an inferior point connected to asuperior-most point of the first posterior surface, the second posteriorsurface extending superiorly from the inferior point to a superior-mostpoint to define an arc having a magnitude of about 45 degrees, wherein(i) the condyle surface in the sagittal plane has a first point on thedistal surface, and (ii) the condyle surface in the sagittal plane has asecond point on the second posterior surface, wherein the condylesurface in the sagittal plane between the first point and the secondpoint includes at least five curved surface sections, each curvedsurface section having a radius of curvature having a length differentfrom any other curved surface section.
 15. The orthopaedic kneeprosthesis of claim 14, wherein the at least five curved surfacesections include an anterior-most curved surface section, the radius ofcurvature of the anterior-most curved surface section having a lengthgreater than the radius of curvature of any other curved surface sectionof the at least five curved surface sections.
 16. The orthopaedic kneeprosthesis of claim 15, wherein the length of the radius of curvature ofeach curved surface section posterior to the anterior-most curvedsurface section is less than the length of the radius of curvature of ananteriorly-adjacent curved surface section.
 17. The orthopaedic kneeprosthesis of claim 16, wherein the length of the radius of curvature ofeach curved surface section posterior to the anterior-most curvedsurface section is less than the length of the radius of curvature of ananteriorly-adjacent curved surface section by a distance in the range of1 millimeters to 3 millimeters.
 18. The orthopaedic knee prosthesis ofclaim 14, wherein (i) the at least five curved surface sections includean anterior-most curved surface section and (ii) each of the at leastfive curved surface sections subtends a corresponding angle, the anglesubtended by each of the curved surface sections posterior to theanterior-most curved surface section being less than the angle subtendedby an anteriorly-adjacent curved surface section.
 19. The orthopaedicknee prosthesis of claim 14, wherein (i) the at least five curvedsurface sections include an anterior-most curved surface section and(ii) each of the at least five curved surface sections subtends acorresponding angle, the angle subtended by each of the curved surfacesections posterior to the anterior-most curved surface section beinggreater than the angle subtended by an anteriorly-adjacent curvedsurface section.
 20. An orthopaedic knee prosthesis comprising: afemoral component having a condyle surface that is curved in thesagittal plane, the condyle surface including: an inferior-most point, adistal surface extending posteriorly from the inferior-most point to asuperior-most point, the distal surface defining an arc having amagnitude of about 30 degrees between the inferior-most point of thecondyle surface and the superior-most point of the distal surface, afirst posterior surface connected to the superior-most point of thedistal surface, the first posterior surface extending superiorly andposteriorly away from the distal surface to define an arc having amagnitude of about 15 degrees, and a second posterior surface having aninferior point connected to a superior-most point of the first posteriorsurface, the second posterior surface extending superiorly from theinferior point to a superior-most point to define an arc having amagnitude of about 45 degrees, wherein (i) the condyle surface in thesagittal plane has a first point on the distal surface, and (ii) thecondyle surface in the sagittal plane has a second point on the secondposterior surface, wherein the condyle surface in the sagittal planebetween the first point and the second point includes at least fivecurved surface sections, each curved surface section (i) subtending acorresponding, substantially equal angle having a magnitude greater thanzero degrees and (ii) having a radius of curvature different from anyother curved surface section.